An arrangement of the kind described above is disclosed in the paper of G. Kolberg entitled "Elektronische Motorsteuerung for Kraftfahrzeuge" published in the journal "Motortechnische Zeitschrift", 46th year, Vol. 4, 1985. In this article, an electronic engine control system having an electronic open-loop/closed-loop control unit is described which operates on the operating variable to be open-loop or closed-loop controlled via an electrically actuable actuator. The control unit operates on the operating variable in dependence upon the operating variables of the engine and/or vehicle. This actuator is concerned with a positioning component determining the power of the engine such as the throttle flap or the injection pump of the engine. For this reason, safety means are connected with the positioning component and change their signal condition in dependence upon the particular position of the actuator; that is, the output signal of the safety device defines a jump-like trace in the form of a switching function in one or more specific positions of the actuator. This safety means is shown as switches with the change in signal condition being effected by a change in the switching mode.
Fault conditions of the electronic engine control system are derived from a comparison of the signal conditions and/or from the comparison of the signal conditions with other operating variables. The position of the actuator for which a change takes place in the signal condition is however subjected to mechanical and/or electrical tolerances and the effects of aging. In this way, in an unfavorable case, it is possible that the changes in signal condition are displaced from the predetermined position of the actuator wherein the change in signal condition should have normally taken place so that in a faulty manner, a fault condition of the electronic engine control system is detected or, in the opposite case, is not detected. In this way, the availability or operating reliability of the electronic engine control system is reduced.